Preload is how you adjust the ride height. It does not make the shock stiffer, just longer under load. I leave mine at zero when I am solo, and crank the remote adjuster up when I carry my wife. Rather than count turns I just look at the gap it makes at the top of the spring. I usually go to 8 mm or so.

The rebound adjuster controls how quickly the shock extends. I have not messed with the stock setting much, as it seems pretty close for normal road riding. Too much rebound will cause the shock to 'pack down' over a series of bumps. Too little will produce a 'weave' in a bumpy corner.

A quick way to evaluate front/rear springs and damping is to hold the front brake and bounce firmly on the seat. Both ends should drop and rise at the same rate.

There are more extensive explanations available, but those are the basics.

Worth the read. Yes its a vstrum specific forum but the concepts work for all bikes.

If you feel the need to learn more then pist I put up here is some light reading material. First book very detailed. I don't own the second book but form what I hear its not as detailed but also a great book.